Phosphor devices are used in lighting apparatus wherein the phosphor (component or mixture), i.e. a substance with wavelength-converting properties, e.g. a fluorescent or luminescent substance, is remote from the exciting light source. Therefore, they are also called remote phosphor devices. Remote phosphor devices can be used in various lighting applications, e.g. in RGB projection equipment, generating red (R), green (G) and blue (B) light for coloured video projection. Other possible lighting applications include medical, architectural or entertainment lighting with coloured or white light.
In prior art remote phosphor devices, such as phosphor wheels or LED based illumination devices, a carrier plate or an optical transmitting member is coated with phosphor. The phosphor is excited by exciting light, e.g. visible blue laser light (450 nm), impinging on the phosphor layer. The exciting laser light is wavelength-converted by the phosphor to generate light with longer wavelengths (e.g. broad spectral distribution with a peak at approximately 520 nm for green light).
The wavelength-converted light from the phosphor is collected by an optical transmitting member, e.g. an optical collimator such as a lens made of glass or a compound parabolic concentrator (CPC) or a compound elliptical concentrator (CEC) etc., arranged in front of the phosphor.
In U.S. Pat. No. 7,543,959 an illumination system including a light source and an optical concentrator coated with phosphor is disclosed. Exiting light from the light source, e.g. a light emitting diode (LED), enters the optical concentrator on its larger end face and is concentrated towards its smaller end face. The smaller end face is coated with a phosphor layer, which is exited by the concentrated exiting light. The exiting light is wavelength-converted by and transmitted through the phosphor layer (“transmissive mode” phosphor device).